1. Field of the Invention
The invention relates to a production method for a capacitive sensor unit, particularly for use for an anti-pinch device in a motor vehicle. The invention relates further to a sensor unit of this type.
2. Description of the Background Art
In a modern motor vehicle, windows, doors, and other movable parts are often driven by a motor-driven operating device. To prevent an object, particularly a body part of a vehicle passenger, being pinched between the movable part and a rigid car body part during an actuation, this type of operating device is usually assigned an anti-pinch device, which stops or reverses the actuation when a case of pinching is detected.
Anti-pinch devices often comprise a sensor, which detects where applicable the presence of an object in a critical pinch region in the path of travel of the structural part, to stop the actuation as early as possible before the object is in fact pinched. To detect objects in the pinch region without contact, capacitive sensors are used for this purpose. A capacitive sensor of this type comprises one or more electrodes with which an electric field is generated in the pinch region. To detect a case of pinching, the electrical capacitance is measured and evaluated, which is formed between—possibly several—sensor electrodes and/or between a sensor electrode and the vehicle body acting as ground. In so doing, the effect is utilized that a foreign object intruding into the pinch region, particularly a human body part, changes the electric field and thereby the measured capacitance.
In the case of windows, doors, and similar structural parts in the motor vehicle field, it is advantageous to place the sensor in the immediate vicinity of a closing edge of the structural part or of an opposite closing edge of the vehicle body, which, of course, is directly adjacent to the pinch region. This type of closing edge often has a complex geometric, usually three-dimensional meandering form of in some cases considerable length, particularly in large structural parts such as a trunk lid or a convertible top. The closing edge, moreover, is exposed to unfavorable environmental influences such as water and—in some cases chemically aggressive—dirt.
Capacitive sensors suitable for this intended use therefore must, on the one hand, be producible simply in the case of relatively large dimensioning. The electrode(s) of such sensors, on the other hand, must be reliably protected from water and dirt and be resistant to mechanical stress, to assure sufficient failure safety and lifetime.
In a design known, e.g., from German Pat. No. DE 10 2004 055 476 B3, a sensor unit is produced by coextrusion of the electrodes in a flexible tubular hollow form, particularly a rubber seal. In this design, the electrodes are protected by the hollow form in a watertight manner. As a disadvantage, however, only relatively simple electrode structures can be realized by coextrusion at reasonable cost. It is costly in particular to place a number (particularly more than just two) electrode layers, arranged side-by-side in the longitudinal direction of the carrier and insulated from one another, in the hollow body.